1. Field of the invention
This invention relates to a method for preparing a catalyst precursor for use in methanol synthesis using, as a copper source, copper sulfate recovered from cheap copper etching waste solution.
2. Description of the Related Arts
As a copper source of a catalyst for methanol synthesis, copper nitrate or copper acetate which do not cause contamination of catalytic poison is employed in many cases. Thus, the total cost for preparing the catalyst becomes significantly high.
The present inventors' group previously provided a method of preparing a basic copper carbonate which is a catalyst precursor using cheap copper sulfate as a starting material in Japanese Patent Application Laid-Open No. 9809/1989.
The basic copper carbonate as a catalyst precursor obtained from copper sulfate according to the above method can be suitably employed for preparing a catalyst for methanol synthesis at low cost. However, from an industrial viewpoint, it is important to develop a method of preparing a catalyst precursor at a lower cost.
Recently, attention has been paid to the fact that copper sulfate recovered from etching waste solution is much cheaper than the conventional and commercially available copper sulfate. It has been required to develop techniques for utilizing the recovered copper sulfate as a source of copper for preparing a catalyst for use in methanol synthesis.
According to an investigation by the present inventors it wa found that copper sulfate recovered from a copper etching waste solution usually contains the mother liquor in the amount of more than 10%, and it cannot be used as the starting material for preparing a catalyst precursor without any treatment. That is, a large amount of excess sulfuric acid is contained in the copper etching waste solution, and various chemicals are also contained therein to control the etching rate or to improve the characteristics of the etching solution. Thus, it was found that these compounds have harmful influence to the final catalyst to be prepared.
In U.S. Pat. No. 4,659,555, there is disclosed a method of preparing a basic copper carbonate by using copper (II) chloride recovered from a copper etching waste solution. However, in the basic copper carbonate obtained by the above method, chlorine and sodium which become catalyst poisons in a methanol synthetic reaction are contained in amounts that exceed the allowable concentration. Therefore, the said basic copper carbonate is not suitable as a starting material for a methanol synthesis catalyst.